The present invention relates to a stereo/monaural switching circuit and an integrated circuit, such as a sound generator integrated circuit, which has the stereo/monaural switching circuit and can be mounted in both an apparatus for stereophonic reproduction and an apparatus for monaural reproduction.
In the case of manufacturing an audio apparatus such as a mobile phone, in order to reduce the manufacturing cost, a sound generator LSI (large scale integrated circuit), which can correspond to both of stereophonic reproduction and monaural reproduction, is manufactured and then the sound generator LSI is used to manufacture both an apparatus for stereophonic reproduction and an apparatus for monaural reproduction.
FIG. 4 is a block diagram illustrating an example of the configuration of an output unit of such a sound generator LSI described above. In the sound generator LSI, loudspeaker amplifiers 11 and 12 serve to drive respective loudspeakers (not shown) connected to loudspeaker terminals 31 and 32 with power supplied through power terminals 21 and 22, respectively. The preamplifiers 41 and 42 serve to drive the loudspeaker amplifiers 11 and 12 on the basis of input signals, respectively. In the sound generator LSI, power AVDD is supplied to circuits, such as the preamplifiers 41 and 42, other than the loudspeaker amplifiers 11 and 12, through power terminals provided separately from the power terminals 21 and 22.
Each of the loudspeaker amplifiers 11 and 12 and the preamplifiers 41 and 42 for driving the loudspeaker amplifiers 11 and 12 has an active state in which an input signal is amplified and is then output, and a power-down state in which an amplifying operation is not performed and power consumption is extremely low. Each of the loudspeaker amplifier 11 and the preamplifier 41 located at a stage prior to the loudspeaker amplifier 11 is in the active state when a power down control signal PDL, which is supplied from a host CPU (not shown) located outside the sound generator LSI, has a value of ‘0’ and is in the power-down state when the power down control signal PDL has a value of ‘1’. In the same manner, each of the loudspeaker amplifier 12 and the preamplifier 42 located at a stage prior to the loudspeaker amplifier 12 is in an active state when the power down control signal PDR supplied from the host CPU has a value of ‘0’ and is in a power-down state when the power down control signal PDR has a value of ‘1’.
An adder 50 is a circuit that mixes an L-channel sound signal SL and an R-channel sound signal SR with each other, which are supplied from a sound generating unit (not shown) within the sound generator LSI, and then outputs the mixed signal. An analog switch 61 selects an output signal of the adder 50 when a monaural/stereo control signal M/S supplied from the host CPU is ‘1’, and then supplies the output signal of the adder 50 to the preamplifier 41. On the other hand, the analog switch 61 selects the L-channel sound signal SL when the monaural/stereo control signal M/S has a value of ‘0’, and then supplies the L-channel sound signal SL to the preamplifier 41.
Hereinbefore, the configuration of the output unit of the sound generator LSI has been described.
The sound generator LSI may be mounted in both an apparatus for stereophonic reproduction, which is provided with loudspeakers corresponding to two channels of L and R, and an apparatus for monaural reproduction, which is provided with one loudspeaker. In the case in which the sound generator LSI is mounted in the former apparatus for stereophonic reproduction, the loudspeaker terminals 31 and 32 of the sound generator LSI are connected to the L-channel loudspeaker and the R-channel loudspeaker, respectively, and both of the power terminals 21 and 22 are connected to a power supply. Moreover, in the apparatus for stereophonic reproduction, the host CPU provides the monaural/stereo control signal M/S having a signal value of ‘0’ to the sound generator LSI. Then, in the sound generator LSI, the L-channel sound signal output from the sound generating unit is amplified by the preamplifier 41 and the loudspeaker amplifier 11 and the R-channel sound signal is amplified by the preamplifier 42 and the loudspeaker amplifier 12, and thus stereophonic reproduction sounds are output from the loudspeakers corresponding to two channels of L and R. In addition, when sound reproduction is not performed because, for example, there is no sound signal to be reproduced, power down control signals PDL and PDR each having a signal value of ‘1’ are output from the host CPU. As a result, each of the loudspeaker amplifiers 11 and 12 and the preamplifiers 41 and 42 becomes in the power-down state, which allows power consumption of the power supply to be saved.
On the other hand, in the case in which the sound generator LSI is mounted in the apparatus for monaural reproduction, the loudspeaker terminal 31 of the sound generator LSI is connected to a loudspeaker. Moreover, in the apparatus for monaural reproduction, the host CPU provides the monaural/stereo control signal M/S having a signal value of ‘1’ to the sound generator LSI. Then, in the sound generator LSI, a signal, which is obtained by mixing the L-channel sound signal and the R-channel sound signal with each other, output from the adder 50 is amplified by the preamplifier 41 and the loudspeaker amplifier 11, and thus monaural reproduction sounds are output from the loudspeaker connected to the loudspeaker terminal 31. The host CPU causes the power down control signal PDR to have a value of ‘1’ all the time, in order to save the power consumption by causing the loudspeaker amplifier 12 and the preamplifier 42, which are not used, to be in a power-down state. In addition, when the sound reproduction is not performed, the host CPU causes the power down control signal PDL to have a value of ‘1’ so as to cause the loudspeaker amplifier 11 and the preamplifier 41 to be in a power-down state, thereby saving the power consumption.
As described above, when a known sound generator LSI is mounted in the apparatus for stereophonic reproduction, the known sound generator LSI outputs sound signals, which are generated by the sound generating unit, as stereophonic reproduction sounds, and when the known sound generator LSI is mounted in the apparatus for monaural reproduction, the known sound generator LSI outputs sound signals generated by the sound generating unit as monaural reproduction sounds. In addition, when the known sound generator LSI is mounted in the apparatus for monaural reproduction, the known sound generator LSI causes a loudspeaker amplifier and a preamplifier, which are not used, to be in a power-down state, thereby saving the power consumption. However, a host CPU in the apparatus for stereophonic reproduction supplies the monaural/stereo control signal M/S having a signal value of ‘0’ to the sound generator LSI, while a host CPU in the apparatus for monaural reproduction supplies the monaural/stereo control signal M/S having a signal value of ‘1’ to the sound generator LSI. Further, the host CPU in the apparatus for stereophonic reproduction is to perform ‘0’/‘1’ switching operation with respect to the power down control signals PDL and PDR in correspondence with whether or not to reproduce a sound, while the host CPU in the apparatus for monaural reproduction is to cause the power down control signal PDR to have a value of ‘1’ all the time and is to perform ‘0’/‘1’ switching operation with respect to only the power down control signal PDL in correspondence with whether or not to reproduce a sound. In the known technique described above, since control operations of the host CPU with respect to the sound generator LSI are different between the apparatus for stereophonic reproduction and the apparatus for monaural reproduction, there has been a problem in that a control program stored in a program memory of the host CPU needs to be changed depending on which apparatus the sound generator LSI is mounted.